The present invention relates generally to a tool for installing fasteners, and in particular to a wrench or socket for locking fasteners.
Various systems for locking threaded fasteners have been developed. Some locking fasteners rely on swaging material from a nut or collar into a recess on a bolt or shear pin. One such system is disclosed in U.S. Pat. No. 4,601,623 issued to Wallace. The locking fastener of Wallace includes a shear pin or bolt with exterior threading to engage the axial bore of a nut or collar. The nut has a base and an elliptical end portion. The elliptical end portion is engaged by an installation tool, which is rotated to thread the nut on the bolt. The elliptical portion of the nut is designed to be swaged or deformed by the tool when a specified load between the nut and the bolt is reached and a predetermined torque is applied. The deformation results in the end portion assuming a circular shape, which ensures that only the predetermined torque will be applied, since the installation tool can no longer rotate the nut after deformation is complete. Further, the nut and bolt are locked together by the swaged material of the nut which fills recesses in the threading on the bolt.
The installation tool disclosed in Wallace has an elliptical bore adapted to engage the end portion of the nut. Engaging the nut with the tool and rotating the tool applies torque to thread the nut onto the bolt. Once a predetermined load is reached, the nut is set and the tool rotates further thereby applying radial compression to deform the nut inward toward the bolt. The deformation of the end portion of the nut continues until the end portion has a circular shape and the tool rotates freely on the nut.
One drawback to the installation tool shown in Wallace and others known in the art is a tendency to "cam off" or to be forced away from the nut during fastening. The end portion of the nut resists being deformed and forces the installation tool away from the free end of the nut. This causes the installation tool to become disengaged from the nut and slip when the nut is being tightened. Thus, it becomes difficult to completely deform the nut and properly lock the nut and bolt together. This tendency is emphasized since this type of locking fastener is often installed in mass quantity with automatic power torque wrenches.
The cam off condition may be overcome, but additional force is required to hold the tool in engagement with the nut. For example, pressure must be applied to the end of the tool to force the tool to engage the nut. Therefore, the cam off condition makes securely fastening the nut and bolt of Wallace difficult.
Another locking fastener system is disclosed in U.S. Pat. No. 4,383,353 issued to Stencel. The locking fastener of Stencel comprises a collar with an interior bore threaded for engagement with a pin. On its exterior, the collar has three lobes that extend radially outward from the collar for engagement with an installation tool. The collar is threaded onto the pin, and at a predetermined load the lobes on the collar deform radially inward to lock the collar and the pin together. The installation tool rotates freely on the collar once the lobes have been deformed.
The installation tool used in the system of Stencel experiences a cam off condition similar to the Wallace tool when the lobes are deformed. The lobes resist being compressed inward and force the installation tool in other directions where there is less resistance. Typically, the installation tool is forced upward and away from the collar when the lobes are under compression. This in turn causes the installation tool to slip off of the collar. Thus, the cam off condition makes it difficult to deform the lobes and lock the collar and pin together.
As a result there is need for an installation tool that reduces or eliminates the cam off condition, and allows the user to easily and efficiently fasten a deformable nut or collar and a bolt together.